Various centrifuges have been used to separate a crystalline or granular material from a liquid carrying the crystalline or granular material. Such centrifuges are typically used in a continuous process in which the combined liquid and solid material is continuously fed into and discharged from the centrifuge. The continuous process is distinguished from a batch process in which a batch of liquid and solid material is fed into the centrifuge. After the materials are separated, the centrifuge is stopped and the separated materials are removed before another batch is loaded into the centrifuge. Both the continuous and batch separation processes are also considered to dry the solid material. The separation process is used in a wide range of applications including the production of soap powders, coal, gypsum, plastic granules, potash, salt, food products, and dairy products.
Industrial centrifuges may be classified according to how they separate the liquid and solid materials. In screen centrifuges, the centrifugal acceleration causes the liquid to pass through a screen through which the larger solid material cannot pass. In decanter centrifuges, there is no screen to physically separate the liquid and solid materials. Instead, the liquid and solid materials are separated by the centrifugal acceleration. The clearing of the liquid typically takes place in the cylindrical portion of the bowl of a decanter centrifuge, whereas the dewatering of the solids via filtration or compression occurs in the conical portion of the bowl.
The inside of a bowl of a centrifuge must be cleaned occasionally prior to start up or after use in order to remove materials which have accumulated along the bowl wall and have not been discharged. Preferably, this clean up is performed without disassembly of the centrifuge. Centrifuges have been cleaned using various methods, such as those disclosed in U.S. Pat. Nos. 4,036,426, 4,978,331, and 5,397,471.
Decanter centrifuges used in the food processing industry require special machinery for processing food and dairy products. For example, machinery used in processing dairy products should not have metal to metal contacts exposed to the dairy products. All areas of the machine that are exposed to the dairy products, including seals, should be washable. There should be no places where product can collect and allow bacteria to grow.